1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method of the same.
2. Description of the Related Art
A flash memory in which data can be maintained even when power is turned off is employed not only for mobile devices, such as cellular phones, but also for FPGAs (Field Programmable Gate Arrays) by embedding it in logic circuits. Especially when a flash memory is embedded in a logic circuit and is employed as in an FPGA, manufacturing processes for the memory cell and for the logic circuit must be compatible to prevent defects in a logic embedded memory which is to be shipped as a product.
In some cases, before the logic embedded memory is shipped as a product or at the time it is actually used, the breakdown voltage of a tunnel insulating film constituting the flash memory is monitored. A tunnel insulating film, however, is formed under a floating gate. Thus, in order to monitor the breakdown voltage by applying a voltage from above and below the tunnel insulating film, a conductive plug should be brought directly into contact with the floating gate without contacting a control gate, and a test voltage should be applied between the conductive plug and a semiconductor substrate.
Therefore, for the above described logic embedded memory, it is important how the process for forming a conductive plug, which contacts the floating gate, is combined with the process for manufacturing a peripheral logic circuit.
According to a technique disclosed in patent document 1, a floating gate and a control gate are electrically connected at an area provided in a peripheral circuit region, and the laminated structure of each gate is employed as a single gate electrode in this peripheral circuit region.    (Patent Document) Japanese Patent Laid-Open Publication No. Hei 6-97457